The present invention relates generally to liquid crystalline light modulating devices, and more specifically to new phase-separated polymeric-liquid crystalline display materials and cells which exhibit multiple stable states after being subjected to a suitable electric field pulse. Depending upon the magnitude and shape of the electric field pulse the optical state of the material can be changed to a new stable state which reflects any desired intensity of colored light along a continuum of such states, thus providing a stable "grey scale."
In the above-noted patent application Ser. No. 07/694,840, now abandoned, incorporated herein by reference, a new liquid crystalline material is disclosed which comprises phase-separated polydomains of polymer network dispersed in liquid crystal. The liquid crystal is a chiral nematic having positive dielectric anisotropy and the polymer is present in an amount less than about 10% by weight based on the combined weight of liquid crystal and polymer. Under different field conditions the material exhibits different optical states. For example, the material can operate either in the mode of being light scattering in a field-OFF condition and clear in a field-ON condition or in the reverse mode of being clear in the field-OFF condition and light scattering in the field-ON condition. In both instances, the material is haze-free at all viewing angles when in the clear state. The material can also be prepared to exhibit bistability, where the application of a low electric field pulse results in a light scattering state and the application of a high electric field pulse, i.e., an electric field high enough to momentarily homeotropically align the liquid crystal directors, drives the material to a light reflecting state that can be any preselected color. The material is bistable because the light scattering and light reflecting states remain stable after the field is removed.
It has now been found that when electric field pulses of various magnitudes below that necessary to drive the material from the stable reflecting state to the stable scattering state will drive the material to intermediate states that are themselves stable. These multiple stable states indefinitely reflect colored light of an intensity between that reflected by the reflecting and scattering states. Thus, depending upon the magnitude of the electric field pulse the material exhibits stable grey scale reflectivity.